Joints pose problems in a variety of situations. For example, cracks and joints in concrete slabs present a difficult maintenance problem during the early life of a structure because of the concrete's ongoing shrinkage. Since shrinkage within the concrete mass occurs over a long period of time, cracks and joints continue to grow in width long after the slab's installation. Exposed surfaces of concrete slabs subjected to repeated impact loads, such as those produced by hard wheel tires on industrial lift trucks, are susceptible to localized failure at the unprotected edges of cracks and joints because of the inherent brittleness of concrete and its weakness in both tension and shear. The breaking and crushing type failure at these unprotected edges typically caused by such exposure is generally referred to in the art as "spalling".
To reduce the likelihood of edge spalling, joints and cracks are routinely filled with sealant materials in an effort to eliminate edge exposures. Various liquid plastics including epoxies, urethanes and polyureas are available as joint fillers. The filler's ability to accommodate any subsequent slab shrinkage will be dictated by its elastic and adhesive bonding properties. While the stresses induced by slab shrinkage are resisted both in the body of the filler material and at its bonding interfaces with the concrete, eventually the tensile strength of the system can be exceeded giving rise to a phenomenon called "re-cracking". If the filler is a rigid, high-strength, high-adhesive material, the re-cracking will occur in the weakest layer of concrete adjacent to the joint. Such re-cracking creates the very same condition the filler was intended to rectify, i.e., concrete edge exposure. In an attempt to avoid such re-cracking failures in the adjacent concrete, semi-rigid, low-adhesive types of filler materials have been formulated, wherein the concrete bonding interfaces of the filler are adhesively weaker than the tensile strength of either the filler or the adjacent concrete. However, when sufficiently stressed by the concrete's shrinkage, re-cracking occurs at the filler/concrete interface, again resulting in concrete edge exposure and susceptibility to spalling under impact loading.
Various joint filling systems have also been proposed in an effort to deal with the foregoing shrinkage-induced spalling problem. Some systems include the use of plastic divider strips in an enlarged spalling repair patch, or insert elements imbedded in the filler during joint installation, all with the goal of causing re-cracking to occur within the filler itself. For example, in U.S. Pat. No. 4,875,802, joints within structural concrete bodies are filled with rigid or semi-rigid fillers to avoid adjacent concrete layer or re-cracking and protect the concrete surface edges of the joints against spalling by repeated impact loading. Inserts embedded in the fillers locationally restrict stress-induced fracture to the joints and in spaced relation to the concrete bonding interfacing interfaces of the fillers so as to maintain a filler protection for both concrete edges. However, there are problems associated with this system. First, the insert must be held in position while the filler is deposited. Second, the filler can migrate into the crack beneath the open joint. If this occurs, the filler can bond the joint or crack sufficiently to relocate the eventual re-cracking back into the adjacent concrete.
In order to overcome these problems, U.S. Pat. No. 5,088,256, discloses a method and system for finishing a joint in concrete. The bottom of the joint is provided with a seal of cement-like material which extends completely across the bottom thereof and fills the crack or fracture line beneath the joint. The lower edge of an insert is inserted partially into the cement-like seal which is in the form of a quick setting sand and cement mixture which has high compression strength and low tensile strength, and which will adhere to concrete surfaces but will not adhere to the insert. The insert is retained in a centered position in the joint by a plurality of spring clips fitted over the insert. The space above the bottom seal on each side of the insert is then filled with a filler of an epoxy or similar material which encapsulates the spring clips and fills the joint on both sides of the insert. However, this approach requires two different materials, a plurality of insert components and extra labor to install same.